The present invention relates generally to the field of combinatorial chemistry and, in preferred applications, to the field of combinatorial materials science. In particular, the invention relates to systems and methods employing microfluidic devices in chemical processes, for characterizing and optimizing such chemical processes and for identifying materials that enhance such chemical processes. Preferred embodiments of the invention relate to microchemical processing systems, to diffusion-mixed microreactors, and to methods for identifying or optimizing heterogeneous catalysts.
Combinatorial chemistry refers generally to methods for synthesizing a collection of chemically diverse materials and to methods for rapidly testing or screening this collection of materials for desirable performance characteristics and properties. Combinatorial chemistry approaches have greatly improved the efficiency of discovery of useful materials. For example, material scientists have developed and applied combinatorial chemistry approaches to discover a variety of novel materials, including for example, high temperature superconductors, magnetoresistors, phosphors and catalysts. See, for example, U.S. Pat. No. 5,776,359 to Schultz et al. In comparison to traditional materials science research, combinatorial materials research can effectively evaluate much larger numbers of diverse compounds in a much shorter period of time. Although such high-throughput synthesis and screening methodologies are conceptually promising, substantial technical challenges exist for application thereof to specific research and commercial goals.
Microfluidics refers generally to the field of miniaturized fluidic systems. Microfluidic systems have been designed to perform similar tasks as larger scale commercial fluid systems, and have included a number of different microcomponents such as fluid-distribution channels, valves, pumps, motors, mixers, heat-exchangers, condensers, evaporators, chemical reactors, chemical separators, sensors and actuators, among others. When microfluidic systems are integrated with microelectronics, the integrated systems are typically referred to as microelectromechanical systems (MEMS). When microfluidic systems include a chemical reactor and/or a chemical separator, the systems can be referred to as chemical processing microsystem. Microfluidic systems have typically been fabricated using technology known in connection with integrated circuit fabrication.
A number of chemical processing microsystems have been developed to effect chemical and/or biochemical conversions, alone or in combination with other unit operations such as separation and analysis. See, for example, Ehrfeld et al., Potentials and Realizations of Microreactors, DECHEMA Monographs Vol. 132, pp. 1-28 (1995) and references cited therein. A microreactor is a common component of such chemical processing microsystems, and a number of different microreactor designs have been developed to date. One type of microreactor design includes microchannels in which a reaction occurs as a fluid moves through one or more relatively long channels of relatively small hydraulic diameter. Microchannels offer a large surface area to volume ratio and, when coupled with microscale heat exchangers, offer exceptional temperature control for exothermic or endothermic reactions. Exemplary channel-type microreactors are disclosed in U.S. Pat. No. 5,811,062 to Wegeng et al., U.S. Pat. No. 5,534,328 to Ashmead et al., U.S. Pat. No.,5,690,763 to Ashmead et al., Tonkovich et al., The Catalytic Partial Oxidation of Methane in a Microchemical Reactor, AIChE 2nd International Conference on Microreaction Technology, pp. 45-53 (1998), Honicke et al., Heterogeneously Catalyzed Reactions in a Microreactor, DECHEMA Monographs Vol. 132, pp. 93-107 (1995), and van den Berg et al., Modular Concept for Miniature Chemical Systems, DECHEMA Monographs Vol. 132, pp. 109-123 (1995) Cell-type microreactors, in which a reaction occurs while a fluid resides in a cell, have likewise been employed. Exemplary cell-type microreactors are disclosed in U.S. Pat. No. 5,843,385 to Dugan, U.S. Pat. No. 6,603,351 to Cherukuri et al., PCT Application WO 98/07206 of Windhab et al., and van den Berg et al., Modular Concept for Miniature Chemical Systems, supra. Microreactors that provide passive mixing and reaction of reactants in “Y”-shaped or, “T”-shaped microchannels are disclosed in Burns et al., Development of a Microreactor for Chemical Production, AIChE 2nd International Conference on Microreaction Technology, pp. 39-44 (1998), and in Srinivasan et al., Micromachined Reactors for Catalytic Partial Oxidation Reactions, AIChE Journal, Vol. 43, No. 11, pp.3059-3069 (1997). Microreactors for heterogenous phase reactions, such as gas-liquid or gas-solid reactions, are reported in Lowe et al., Microreactor Concepts for Heterogeneous Gas Phase Reactions, AIChE 2nd International Conference on Microreaction Technology, pp. 63-73 (1998). Reactors specifically designed for certain classes of reactions, such as electrochemical reactions or photo-induced reactions have likewise been contemplated. See, for example, Matlosz et al., Microsectioned Electrochemical Reactors for Selective Partial Oxidation, AIChE 2nd International Conference on Microreaction Technology, pp. 54-59 (1998).
Contemplated applications for such chemical processing microsystems include end-use production of hazardous chemicals, process characterization and optimization, and combinatorial chemistry. While combinatorial chemistry applications have been contemplated, the various chemical microreactor designs reported to date, however, have not been incorporated into systems suitable for large-scale, or even moderate-scale, combinatorial chemistry research, and particularly, for combinatorial material science research directed to heterogeneous catalyst screening for identification and/or optimization. For example, although parallel-type reactors and microreactors have been reported (see, e.g., U.S. Pat. No. 3,431,077 to Danforth, U.S. Pat. No. 4,099,923 to Milberger, U.S. Pat. No. 5,603,351 to Cherukuri et al. and PCT Application WO 98/07206 of Windhab et al.), none of these reactors are satisfactory for combinatorial materials science applications. These and other microreactor designs known in the art do not address important concerns such as the loading, and/or unloading of larger numbers of candidate materials (e.g., catalysts) for screening, the supplying of reactants to a plurality of microreactors, the controlling of the reaction conditions in a plurality of microreactors, and/or the evaluating of candidate materials for specific properties of interest (e.g., catalytic activity). Known microreactors also have common limitations, for example, with respect to a low throughput (e.g., the number of catalysts that can be screened over a given period of time), a narrow distribution of heterogeneous catalyst contact times, a large amount of each (often expensive) candidate catalyst required to effect the chemical conversion, the potential inherent negative influence of microreactor materials on a reaction of interest, a high degree of complexity, a lack of flexibility for analyzing the results of the chemical conversion, and, in some cases, a lack of scalability of research results to production-scale systems.
The present invention, as described in detail below, overcomes many, if not all of such shortcomings.